...alternatively, you could use the pre-existing settings framework in Visual Studio. It won't suit a custom XML file, but if the idea is to read/write application settings from/to an XML file, it does most of the hard work for you. It will select a suitable location for such a file, auto-generate code such that it's very easy to interact with settings and it abstracts away the file IO side of things. Definitely worth a peek to check that you're not re-inventing it:
http://msdn.microsoft.com/en-us/library/c9db58th.aspx